METABOLIC ACTIVITY OF NERVOUS SYSTEM 



369 



UREA AND AMMONIA NITROGEN 



Although the observations on the urea and ammonia nitrogen 

 are not numerous, yet it appears certain that the content of 

 ammonia is far more constant than that of urea. The amount 

 of ammonia here found is shghtly higher than that found by 

 Levene and Stookey ('03) in the dog's brain, in which they report 

 10 mg. ammonia nitrogen per 100 grams of mbist brain weight. 

 Recently Marshall and Davis ('14) determined by their urease 

 method the urea content of various organs and tissues in the dog. 

 The brain gave 28 mg. urea nitrogen per 100 grams of fresh tissue 

 or practically the combined values of urea and ammonia nitrogen 

 found in the rat brain. Since Marshall and Davis did not at- 

 tempt to eUminate the ammonia nitrogen from the materials 

 previous to urea determinations, the value given by them as the 

 urea nitrogen may have been in fact that combined values of the 

 urea and the ammonia nitrogen. If such were the case my own 

 results on the rat agree \\dth those for the dog very closely. I 

 have made also a short series of observations on the non-protein 

 nitrogen content in other organs than the brain of the adult 

 rat and the results thus obtained are given in table 4. 



TABLE 4 



As is shown in table 4, with the exception of the blood, the 

 non-protein nitrogen in the brain is least as compared \^^.th the 

 other three organs. However, when the comparison is made 

 between total nitrogen content of the organ and content of non- 

 protein nitrogen, the brain gives a higher figure than either the 



